The present invention relates to a method of manufacturing a semiconductor device and, more particularly, to a method of forming an embed-type isolation region which is formed by embedding an insulation film in a trench formed in a semiconductor substrate.
LOCOS (Local Oxidation of Silicon) method has generally been used as a conventional isolation method. The LOCOS method is a process of thermally oxidizing a SiN film formed in an element forming region on a semiconductor substrate and forming an oxide film only in an isolation region.
Miniaturization of devices of a semiconductor integrated circuit has recently been improved rapidly, and an oxide film formed in the isolation region is decreased in thickness. If the thickness of the oxide film decreases, a transition region called a bird's beak occurs continuously in the oxide film formed between an element region and an isolation region, thereby making it difficult to isolate the devices.
To electrically isolate the miniaturized devices, a so-called STI (Shallow Trench Isolation) method has been used. Since, in this method, a trench is formed in an isolation region on a semiconductor substrate and an insulation film such as an oxide film is embedded in the trench, there occurs no problem of thinning the oxide film.
Thus, the STI method has the advantage of preventing a bird's beak, which was caused in the conventional LOCOS method, from occurring. However, it is essentially excellent in miniaturization but has the following problem which is hardly caused in the LOCOS method.
When a material having a high contraction rate is embedded into the trench, its volume is reduced in the subsequent high-temperature heat treatment process, with the result that a thermal oxide film is likely to come off that side of a silicon substrate which corresponds to the inner side of the trench to cause a gap between the thermal oxide film and the inner side of the trench.
FIGS. 1A and 1B are cross-sectional views of a conventional method for manufacturing a semiconductor device.
Referring to FIG. 1A, a plurality of trenches 41 are formed on a silicon substrate 40 and a thermal oxide film 42 is formed on the bottom and sides of each of the trenches 41. After that, a TEOS (Tetra-Ethyl-Orth-Silicate) oxide film 43 serving as an embedded material is deposited on the entire surface of the substrate 40 including the inside of the trench 41 and then flattened.
The TEOS oxide film 43 undergoes high-temperature heat treatment at 1190.degree. C. in a nitrogenous atmosphere. The objective of the high-temperature heat treatment is to improve the resistance of wet acid processing to the embedded oxide film, prevent the oxide film from decreasing in thickness, and control a phenomenon in which a crystal defect occurs in the silicon substrate.
However, the TEOS oxide film 43 is decreased in volume by the above high-temperature heat treatment and, as shown in FIG. 1B, the thermal oxide film 42 comes off the inner surface of the trench 41 to cause a gap 44 between the film 42 and trench 41.
If a wiring material enters the gap 44 in the subsequent wiring process, it is difficult to remove.
For example, as shown in FIG. 2, if a wiring material 53 remains between wirings 51 and 52, these wirings will be short-circuited.
Furthermore, in a transistor having the above-described gap, a current will leak from a PN junction of regions contacting the gap, thereby causing a malfunction of the integrated circuit.